<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        //真：true 、非零数字、非空字符串、非空对象
        //假：false、数字零、空字符串、空对象、undefined
        var a=0;
        if(a){
            alert('真');
        }
        else{
            alert('假');
        }
    </script>
</head>
<body>

</body>
</html>